The invention relates to methods and equipment for service advertising and user authorization in a telecommunication system.
Two trends in telecommunications act as a driving force for the invention. One of the trends is the fact that distinctions between different communication technologies and terminal equipment will be increasingly blurred, and a single multi-mode terminal will be used to access a wide variety of different services, such as e-mail, web surfing, radio and TV programs, etc. Multimode terminals have several alternative access techniques, such as any combination of cellular radio (GSM, GPRS, UMTS, etc.), DAB, DVB, WLAN, etc. The other trend is that backbone networks are increasingly based on Internet Protocol (IP).
In a GSM environment, operator (network) selection is simple: a subscriber of a given network cannot normally select another operator in his/her home country. When roaming abroad, most mobile phones select the strongest carrier unless the user manually overrides the phone's automatic selection.
A first problem with multi-mode terminals is that a manual network selection is too cumbersome, and an automatic selection based on signal strength is not sufficient. Thus there is need for more advanced network selection. Such an advanced network selection in turn causes a second problem, namely the fact that a terminal (or its user) should be authenticated in several networks before the terminal can select a network. The multiple authentication in turn has a third problem which has not existed in earlier systems, namely a complete lack of trust between a network operator and roaming user. In conventional mobile networks, such as GSM, the network infrastructure is so expensive and extensive that a roaming user, seeing an operator's name on the display of the terminal, can automatically trust that the operator is what it claims to be. In other words, it is infeasible to set up a GSM network for fraudulent purposes, such as eavesdropping. In WLAN environments, for example, this assumption may not be valid. For example, it is possible for an eavesdropper to set up a WLAN system in places where important information can be obtained. If the eavesdropper's system offers WLAN services that seem more attractive than those of its competitors, a terminal may select an untrustworthy network, and data privacy will be lost. Thus a novel problem is that not only must a network operator authenticate a roaming user but the user must also be able to establish trust with the network operator.